Temperature dependence on the structural fluctuations of Zundel cation, H5O2+, and its isotopomers, D5O2+ and T5O2+, have been studied using path integral molecular dynamics simulations in which nuclear quantum effect is fully taken into account. It has been found that the fluctuations of hydrogen-oxygen and oxygen-oxygen distances, which are relevant to the hydrogen bonded structure, grow drastically as the temperature increases within the range of investigation between 100 K and 900 K. The fluctuation with respect to the position of non-bonded hydrogen also increases substantially as the temperature increases. The temperature dependence on the fluctuation is greater for D5O2+ or T5O2+ than that of H5O2+, since the zero-point effect of the former is less than the latter. (C) 2013 AIP Publishing LLC.